1. Field of the Invention
The present invention relates to a process for improving the adhesion of a polyimide layer to an underlying metal surface, such as a substrate containing a pattern of metallization, e.g. copper.
2. Description of the Prior Art
It is known that polyimides formed by the thermal curing of polyimide precursors, such as polyamic acids, can be used as passivation dielectrics on semiconductor devices. See, for example, U.S. Pat. No. 4,590,258, issued to Linde, et al., on May 20, 1986. A problem arises, however, in that polyimides adhere poorly to metal surfaces, enhancing moisture penetration and oxidation at the interface, which result in a loss of its passivation function.
Techniques are known in the art for improving the adhesion of various polymers to underlying substrates. For example, U.S. Pat. No. 4,103,045, issued to Lesaicherre, et al., on Jul. 25, 1978, describes a process for bonding a photoresist polymer to an inorganic oxide layer, by applying to the layer a solution of a selected aminosilane or cyclopolysiloxazane. Similarly, U.S. Pat. No. 4,529,618, issued to Ponjee, et al. on Jul. 16, 1985, first treats an inorganic material with an aqueous solution of a 3-aminopropyltrialkoxysilane before applying a photoresist polymer.
It is also known to form silsesquioxane polymers for use as insulating layers in semiconductor devices. For example, in Eur. Pat. Appln., published under No. 0,226,208 on Jun. 24, 1987, an insulating layer is formed by applying to a substrate a prepolymer, and then heating it at a temperature above 400.degree. C. in the presence of oxygen. The prepolymer is prepared by hydrolyzing and polycondensating a mixture of a tetraalkoxysilane, a trialkoxysilane and a dialkoxysilane in a select mole ratio.
In U.S. Pat. No. 4,626,556, issued to Nozue, et al., on Dec. 2, 1986, water is reacted with a trihalogenosilane in the production of a non-amino-containing silsesquioxane polymer, which is used in a mixture with a compound which generates crosslinking-reaction-active species upon irradiation, in the formation of an insulating layer. In U.S. Pat. No. 4,723,978, issued to Clodgo, et al., on Feb. 9, 1988, an organoglass insulating layer is produced by first forming a modified ladder-type silsesquioxane polymer from a silanol solution, and then treating it in an oxygen plasma.
However, none of these approaches involves the formation of a silsesquioxane polymer as an adhesion-promoting layer.